Fixed potential typescript error in examples/axios-typescript

[Svish]

Fixes #238 (hopefully)

[shuding]

Thanks!

[FridgeWalaby]

@Svish @quietshu
My vscode still complains about the next line after () => axios(request!),

{
      ...config,
      initialData: initialData && {
        status: 200,
        statusText: 'InitialData',
        config: request,
        headers: {},
        data: initialData
      }
    }

These lines get the following error:

Argument of type '{ initialData: { status: number; statusText: string; config: GetRequest; headers: {}; data: Data; } | undefined; errorRetryInterval?: number | undefined; loadingTimeout?: number | undefined; ... 14 more ...; compare?: ((a: AxiosResponse<...> | undefined, b: AxiosResponse<...> | undefined) => boolean) | undefined; }' is not assignable to parameter of type 'ConfigInterface<AxiosResponse<Data>, AxiosError<Error>, fetcherFn<AxiosResponse<Data>>>'.
  Types of property 'initialData' are incompatible.
    Type '{ status: number; statusText: string; config: GetRequest; headers: {}; data: Data; } | undefined' is not assignable to type 'AxiosResponse<Data> | undefined'.
      Type '{ status: number; statusText: string; config: GetRequest; headers: {}; data: Data; }' is not assignable to type 'AxiosResponse<Data>'.
        Types of property 'config' are incompatible.
          Type 'GetRequest' is not assignable to type 'AxiosRequestConfig'.
            Type 'null' is not assignable to type 'AxiosRequestConfig'
`
``